A bridge is not a gateway. It will likely have an IP address from DHCP, like other regular devices, so check the Mikrotik router's DHCP lease table first.
The TP-Link might have a static address configured instead (even one in a completely wrong subnet – this doesn't actually affect its function as a bridge). If you don't see it in the Mikrotik "DHCP server" lease list, try an IP scanner app (Mikrotik routers have such a function built in).
(Another way to detect an unknown IP address of a device is to fire up Wireshark on some machine on the bridge's Ethernet side, or even on the Mikrotik, then restart the TP-Link and look for any packets coming from its MAC address – e.g. filtering by eth.src == ab:cd:...
– until you see an ARP packet or something that hints at the TP-Link's IP address.)