Finding specific messages or threads using search tools within Microsoft Teams chat history
Hello, Naglaa
I am Igor and I will be glad to help you with this question :)
Try to disable the settings and then reactive it:
In the Microsoft Teams admin center, select Teams > Teams settings.
Under Search by name, next to Scope directory search in Teams using an Exchange address book policy, turn the toggle Off.
then wait afew moments
Turn on the toggle again and it will should take a few hours to take effect