I have a shitty ISP given wireless-router/modemand i want to use a hAP as a wireless AP instead and turn off the wireless function on the ISP device. What settings would I need to use??

Configure your client settings on the WLAN interface of your router. Then, in the WLAN settings, change your "mode" to AP_BRIDGE, and set your SSID to your desired accesspoint name.

Would I need to bridge the wlan to an ethernet port?

If you will like to use the ethernet port on your client side too, you can bridge. Otherwise, just leave out the bridge.

How would the mikrotik device know to communicate with the ISP modem? I thought you needed to bridge to do that?

Does the ISP modem have a LAN port?

How would the mikrotik device know to communicate with the ISP modem? I thought you needed to bridge to do that?

Please tell us which mysterious MikroTik device you have...
There are differences between the setup of a router and an access point.  The latter normally come with a bridge config already in place.

He wrote he had hap.
Generally every mikrotik device with wlan and level 4 licence at least can be set in the same way - to be an access point.

hello
connect to hAP router with winbox then go to wireless menu and double click on wlan1 then go to wireless tab then set mode ap-bridge then set ssid then set band 2Ghz/b/g/n
Good Luck