Hello...

I have configured Mikrotik Hotspot for public access. It's working perfect.

Now I have two extra AP (TP-LINK) that I don't use. I wonder is it possible configure this AP's to connect (LAN) to Mikrotik so that can serve as Mikrotik Hotspot and expand WiFI network. I read that this is possible with UniFi AP.

Can anyone help me pls,
Thank you

You can do with any access point. TP-Link or Unifi it's doesn't matter what brand you use.
The Access Point is just extend your wireless network coverage and wireless quality it's depend on AP brand.
Hotspot is running on MikroTik Devices, So you can used any Access Point.

I see.
How do I configure that? I can't find any instructions on the internet...

only disable dhcp on tplink.

It's disabled.
What is gateway here - Mikrotik hotspot?