אני רוצה לאשר שהפגישה שלנו מחר בבוקר.

It is understandable, but many native speakers would feel that it is a little incomplete or slightly abrupt in formal writing.

A very clear version would be:

אני רוצה לאשר שהפגישה שלנו היא מחר בבוקר.

The added היא means is. In everyday Hebrew, especially in speech, Hebrew often drops is in the present tense, so the original sentence can still work. But in a sentence like this, adding היא often sounds smoother and clearer.

In polite written communication, people also often say:

רציתי לאשר שהפגישה שלנו מחר בבוקר.

That literally uses past tense (I wanted to confirm) but functions like a softer, more polite I just wanted to confirm.

Because in Hebrew, present-tense sentences often do not use a separate word for is / are.

So:

הפגישה שלנו מחר בבוקר
literally looks like: our meeting tomorrow morning
but it means: our meeting is tomorrow morning

This is very normal in Hebrew.

That said, Hebrew can also include היא here:

הפגישה שלנו היא מחר בבוקר

Both are possible, but adding היא can make the sentence feel clearer or a bit more explicit.

The ש־ means that.

So:

• אני רוצה לאשר = I want to confirm
• שהפגישה שלנו מחר בבוקר = that our meeting is tomorrow morning

Hebrew often attaches this ש־ directly to the next word, so:

ש + הפגישה = שהפגישה

This is very common in Hebrew.

After רוצה (want), Hebrew normally uses an infinitive, just like English often uses to + verb.

So:

• רוצה = want
• לאשר = to confirm

Together:

רוצה לאשר = want to confirm

This is a standard pattern:

• אני רוצה לאכול = I want to eat
• אני רוצה ללכת = I want to go
• אני רוצה לאשר = I want to confirm

The ל־ at the start of לאשר is part of the infinitive form.

Here, לאשר means to confirm.

But this verb can also mean to approve, depending on context.

For example:

• in scheduling: לאשר פגישה = confirm a meeting
• in office or bureaucratic contexts: לאשר בקשה = approve a request

So this is one of those Hebrew verbs whose meaning depends on the situation. In your sentence, because it is about a meeting time, the natural meaning is confirm.

Because in Hebrew, the normal order is:

noun + possessive word

So:

• הפגישה שלנו = our meeting
• הבית שלי = my house
• המורה שלהם = their teacher

Hebrew does not normally put שלנו before the noun the way English puts our before meeting.

So English says:

our meeting

but Hebrew says, more literally:

the meeting of ours

That is why שלנו comes after הפגישה.

This is a very common thing for English speakers to notice.

In Hebrew, a possessed noun often still appears with ה־ when it refers to a specific, identifiable thing:

הפגישה שלנו = our meeting
המכונית שלי = my car

So even though English does not say the our meeting, Hebrew often naturally uses the definite article here.

This is especially common when talking about a specific known item or event, like a scheduled meeting.

Because מחר already means tomorrow by itself, so it does not need a preposition.

Then בבוקר means in the morning:

• ב־ = in
• בוקר = morning
• בבוקר = in the morning

So:

מחר בבוקר = tomorrow morning

This is the normal Hebrew expression.

You do not say something like במחר for tomorrow.

Hebrew word order is somewhat flexible, but not every order sounds equally natural.

The version you have:

אני רוצה לאשר שהפגישה שלנו מחר בבוקר

is natural in terms of order.

You could also say:

אני רוצה לאשר שמחר בבוקר הפגישה שלנו.
or better:
אני רוצה לאשר שמחר בבוקר הפגישה שלנו היא...

But that starts to sound more marked, as if you are emphasizing tomorrow morning.

For a neutral sentence, keeping מחר בבוקר after הפגישה שלנו is very natural.

It is grammatical and understandable, but in real-life polite communication, Hebrew often uses slightly softer wording.

Very common alternatives are:

• רציתי לאשר שהפגישה שלנו מחר בבוקר.
• רק רציתי לאשר שהפגישה שלנו מחר בבוקר.
• אני רוצה לוודא שהפגישה שלנו מחר בבוקר.

A small nuance:

• לאשר = confirm
• לוודא = make sure / verify

So if you are checking the meeting time with someone, לוודא can sometimes sound especially natural.

Still, אני רוצה לאשר is absolutely understandable and not wrong.