you meant to say the shop sells battery, but just don't offer replacement service?

there are other ways to get help:
1. find out from the seller who sold you the board;
2. use google to find out to see if there are users replace/upgrade battery before;
3. find out keychron malaysia contact at fb etc to see if they can help to find replacement for you;
4. join keychron fb page to see if there are users who replace battery before;
5. contact keychron directly to see if they can help.

or, you can help yourself, i.e. check the serial number, specs, dimension, etc. of stock battery, and find it at taobao/aliexpress.

edit: ok our friend have already shared his experience also

Lithium battery can be quite dangerous if you puncture it. I would recommend removing it outside... in case it catch flame.
I would use 100% ethanol to try to dissolve the adhesive.
As for hairdryer.... maybe can try heating from the back. Don't blow it directly to the battery.

I can't seem to find the exact same battery model.
But a battery with similar voltage (3.7V), with similar dimension might be quite common.