You must be a chat administrator to remove members.
Open the chat, click the dot menu and select View members.
Remove Smart members
If the chat uses Smart members (added based on rules), you remove them by editing or removing the rules. In the members list, Smart members have a star next to their names and cannot be removed individually. To remove them, click the dot menu > Remove from chat to delete the rule.
Remove regular chat members
To remove a normal member, click the dot menu next to their name and choose Remove from chat. Confirm and they will be removed from the chat.