We can change the encounter on next Sunday if you will have time.
I am not sure if in the above sentence "will" should be omitted. Not sure how the English grammar describes this kind of conditional sentence if it is conditional anyway.
We can change the encounter on next Sunday if you will have time.
I am not sure if in the above sentence "will" should be omitted. Not sure how the English grammar describes this kind of conditional sentence if it is conditional anyway.
I agree with the comment by Colin Fine that "encounter" is an unusual word for a scheduled event. The word "meeting" would be more usual, or "get-together" if it is a social gathering and several people are involved. The word "appointment" would also be common. Thre are, of course, many terms for different kinds of meetings and events. Wintout context I can't suggest a specific one.
The use of "on next Sunday" suggests that the meeting is already scheduled for next Sunday, and something else about it is to be changed. If the schedule is to be changed from some other day to next Sunday, then "to" should be used, not "on".
You should omit the "will."
In this type of conditional (using if to refer to an possible event in the present or future), the conditional phrase should be in simple present ("if you have time") and the main clause in simple future ("We will change the encounter on next Sunday" or "We can change the encounter on next Sunday").
meeting is probably a better word than encounter - I agree with Colin Fine's comment that encounter sounds strange in this context. I agree with yuankhan that you don't need will - since that was your question. It will be understood that you are wondering whether the other person will have time on the future date you are talking about. Finally, I agree with Don B. that "on" does not sound correct. You should use to if you want to change the time from another day to "next Sunday". But if the event is already scheduled for "next Sunday" and you just want to change the time of day, on still doesn't sound natural (especially when followed by the word next). I would suggest wording it like this:
We can reschedule next Sunday's meeting if you have time.
(if the meeting is already supposed to be on Sunday)
We can reschedule the meeting to next Sunday if you have time.
(if the meeting is currently scheduled for a different day)