غيرت الرقم السري مبارح.

غيرت is the past tense of غيّر meaning to change.

In Levantine, غيرت can be pronounced:

• ghayyart = I changed
• ghayyaret = she changed

Because short vowels usually are not written, the spelling looks the same. In this sentence, the meaning and pronunciation tell you it is I changed.

So:

• غيّر = he changed
• غيرت pronounced ghayyart = I changed

Because Arabic often drops subject pronouns when the verb already makes the subject clear.

So instead of saying:

• أنا غيرت الرقم السري مبارح

speakers very naturally just say:

• غيرت الرقم السري مبارح

Adding أنا is possible, but it usually adds emphasis, contrast, or clarity, like:

• أنا غيرت الرقم السري، مش هو
• I changed the password, not him

Because adjectives usually come after the noun in Arabic.

So:

• الرقم = the number
• السري = the secret

Together:

• الرقم السري = literally the number the-secret

In natural English, we reverse that order and say the secret number or more idiomatically the password / PIN / passcode.

Because in Arabic, adjectives agree with the noun they describe in definiteness.

Since الرقم is definite (the number), the adjective must also be definite:

• رقم سري = a secret number
• الرقم السري = the secret number

This is very normal Arabic adjective agreement.

Literally, الرقم السري means the secret number.

In everyday usage, it often means:

• PIN
• passcode
• sometimes password

A lot of speakers also use كلمة السر for password, especially for website or account passwords.

So the nuance is roughly:

• الرقم السري = often a numeric code, PIN, or passcode
• كلمة السر = password more generally

But in casual speech, people may use الرقم السري quite broadly.

A common Levantine pronunciation would be:

ghayyart er-raʔem es-serri mbāreḥ

A few notes:

• غيرت → ghayyart
• الرقم → often er-raʔem in many urban Levantine varieties
  Some speakers may say something closer to er-raqam
• السري → es-serri
• مبارح → mbāreḥ

Also:

• غ is the gh sound
• ح in مبارح is a stronger, breathier h than English h

This is because of sun-letter assimilation.

The definite article is written الـ, but when the next letter is a sun letter, the l sound assimilates to that letter.

Here:

• الرقم is pronounced er-ra... because ر is a sun letter
• السري is pronounced es-se... because س is a sun letter

So although it is written with الـ, the pronunciation changes.

مبارح means yesterday.

Yes, it is a very common Levantine colloquial word. You may also hear:

• امبارح
• مبارحة in some contexts or areas

Compared with Standard Arabic:

• Levantine: مبارح
• MSA: أمس or البارحة

So مبارح is a strong clue that this sentence is dialect, not formal Standard Arabic.

Yes. Time words like مبارح are fairly flexible.

All of these can work, depending on emphasis:

• غيرت الرقم السري مبارح
• مبارح غيرت الرقم السري
• أنا غيرت الرقم السري مبارح

The original sentence sounds very natural and neutral:
I changed the password yesterday.

Putting مبارح first can give a little extra focus to yesterday.

This sentence is Levantine dialect.

Clues:

• مبارح is colloquial
• there are no case endings
• the style is conversational

A Standard Arabic version could be:

• غيّرتُ الرقم السرّي أمس

A more formal or modern MSA way to say password might also be:

• غيّرتُ كلمة المرور أمس

So the given sentence is clearly the everyday Levantine way.

For I changed, no. A male speaker and a female speaker both say:

• غيرت pronounced ghayyart

So first-person singular past does not change for the speaker’s gender.

But there is one important detail: in writing, غيرت can also represent she changed, because Arabic usually does not write short vowels.

So:

• ghayyart = I changed
• ghayyaret = she changed

In speech, the pronunciation makes it clear.