Welcome @Nayab,
- You could use a choice_filter with: not( contains(${YourJoin}, name) ), see https://getodk.github.io/xforms-spec/#fn:contains.
- There is also an select_one from repeat option to create a choice list directly from a repeat group, see https://docs.getodk.org/form-logic/#generating-select-ones-from-repeats.
More hints and examples can be found with the search function of this forum, esp.
Generate multiple choice alternatives, based on the answers in a repeat - #16 by LN.
Please, also pretest your solution data export (values, labels) for your your final solution.