need help on clearing users from IP pool of router

Hi all, new here and complete noob, sorry if anything i say has any technical mistakes.

We run a retail store with a lot of computers on LAN so we have assigned a small IP pool to allow 60 users to connect to the Wifi so that there are no clashes with the LAN IP addresses. But the issue is that we allow customers to use our wifi if needed, so their device takes up an IP and shows up in the client list for even days after their visit even though theyre never gonna use it again. This has made the Client list reach 60 in a few days, is there a way to clear all the IP leases ? right now any new device that gets connected says 'connected but no internet' because the IP pool is full

Using a TP link router

this is the screen i see https://imgur.com/a/4wQsxzw