A family of Microsoft word processing software products for creating web, email, and print documents.
That is one way of inserting an IF field, but it's rather limiting.
The best way (IMHO) is to create the empty field directly via Ctrl-F9, then populate it with such arguments & parameters as you need. Much can be achieved this way. see, for example:
https://www.msofficeforums.com/mail-merge/40517-how-can-i-write-complex-if_then_else-statement.html
https://www.msofficeforums.com/mail-merge/34045-merge-one-excel-file-into-multiple-word.html
https://www.msofficeforums.com/mail-merge/41848-mail-merge-if.html
https://www.msofficeforums.com/mail-merge/44922-multiple-options-not-displayed-using-if.html
https://www.msofficeforums.com/mail-merge/45135-word-mailing-conditionally-adding-information.html
https://www.msofficeforums.com/mail-merge/37039-if-true-nested.html
See also:
https://www.msofficeforums.com/mail-merge/21803-mailmerge-tips-tricks.html
https://www.msofficeforums.com/mail-merge/42406-if-statements-several-ranges-values-using-mail.html