I would put 'to" there. If you put "to" there you should change "who" to "whom".
Interested in Language
Hi. Do I need to put "to" before the underlined expression? "I would like to assure that an extensive part of Armenia’s population is supporting your national football team who I wish great successes."
I would start it with "I would like to assure you that ...". I would also add "to", change "who" to "whom" and change the last word to "success".
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.
an extensive part of Armenia’s population- I would use a large part/most/the majority, etc.