yàoshi nǐ xiěcuò le, jiù yòng xiàngpí cādiào ba.

要是 means if in a fairly natural, conversational way.

• 要是 + clause, 就 + result is a very common if ... then ... pattern.
• 如果 also means if, but it can sound a little more neutral or formal.
• In everyday speech, 要是 is very common.

So:

• 要是你写错了，就... = If you wrote it wrong / If you make a mistake writing, then...

Here, 了 shows that the action has happened or the mistake has been made.

• 写错 = to write something incorrectly
• 写错了 = wrote it wrong / have written it wrong

This 了 is marking a completed event or a new situation: now the writing is wrong, so the next step is to erase it.

It is not just random decoration. Without 了, the sentence would feel less tied to an actual completed mistake.

写错 is a verb + result complement structure:

• 写 = write
• 错 = wrong, mistaken

Together, 写错 means to write something wrong, to write incorrectly, or to make a writing mistake.

This pattern is very common in Mandarin:

• 看错 = see wrongly / mistake one thing for another
• 说错 = say something wrong
• 听错 = hear wrongly
• 做错 = do something wrong

So 错 tells you the result of the action.

就 links the condition to the result. In this pattern, it often means something like then.

So the structure is:

• 要是 ... ，就 ...
• If ..., then ...

In English, we often leave out then, but in Chinese 就 is very common in this kind of sentence.

So:

• 要是你写错了，就用橡皮擦掉吧。
• If you wrote it wrong, then erase it with an eraser.

You can think of 就 as helping the sentence feel logically connected.

用 means to use and introduces the tool or means.

The pattern is:

• 用 + tool + verb

So here:

• 用橡皮擦掉
• use an eraser to erase it

This is very natural Chinese word order. The instrument comes before the main action.

Similar examples:

• 用笔写 = write with a pen
• 用刀切 = cut with a knife
• 用手机拍 = take photos with a phone

擦掉 is also a verb + result complement structure:

• 擦 = rub, wipe, erase
• 掉 = off, away, removed

So:

• 擦 = rub/wipe
• 擦掉 = wipe off / erase completely

The 掉 shows the result: the wrong writing is removed.

If you only said 擦, it could sound less complete, more like just rubbing.
擦掉 makes it clear that the goal is to get rid of the mistaken writing.

吧 softens the sentence.

Without 吧, the sentence can sound more direct, like a plain instruction:

• 就用橡皮擦掉。 = Then use an eraser to erase it.

With 吧, it sounds more like:

• a suggestion
• gentle advice
• a softened command

So 擦掉吧 is like:

• just erase it
• you can erase it
• go ahead and erase it

It makes the tone friendlier and less harsh.

Yes. In Mainland Mandarin, 橡皮 commonly means eraser.

A few notes:

• In Mainland China, 橡皮 usually means the thing you erase pencil marks with.
• You may also hear 橡皮擦, which is even more explicit: eraser.
• In some contexts, since 橡皮 literally relates to rubber, learners may notice overlap with the English word rubber, but in this sentence it clearly means eraser.

So here, 用橡皮擦掉 definitely means erase it with an eraser.

The object is understood from context.

Mandarin often leaves out things that are obvious. Here, what gets erased is the thing that was written wrong:

• a character
• a word
• a stroke
• the mistaken writing in general

So even though there is no explicit object, the meaning is clear.

If you wanted to say it more fully, you could say something like:

• 就用橡皮把它擦掉吧。
• Then use an eraser to erase it.

But in the original sentence, leaving it unstated is perfectly natural.

It can work either way, depending on context.

Because of 写错了, it often sounds like:

• if you’ve written it wrong
• if you make a mistake writing it

So it can refer to:

1. a specific mistake
   for example, a teacher notices you wrote one character wrong

2. general advice
   for example, someone explaining what to do whenever you write something incorrectly

Mandarin often allows this kind of flexibility, and context tells you which reading is intended.

Yes, in many situations 你 could be omitted if it is already clear who the speaker is talking to.

For example:

• 要是写错了，就用橡皮擦掉吧。

This still sounds natural, especially in conversation or instructions.

However, keeping 你 can:

• make the sentence clearer
• make it more directly addressed to the listener
• add a slightly more personal or instructional tone

So both are possible, but the version with 你 is very normal.