Traditional wired doorbells have a transformer

Mine has the transformer mounted at the power switchboard.
Post #10 shows my setup. The existing transformer powers the wireless door bell and keeps a blue LED lit all the time.
Pushing the button rings the old doorbell and the wireless door bell together.

 

In post #18, the upper drawing shows how your original doorbell must have been wired at one time. The doorbell button you wish to keep MUST have wires there now. Those wires likely go to a transformer and to what once was a doorbell chime. Adding wires or adding power should not be necessary, but since I can't examine what you have I can't say that for sure. Wherever the original doorbell chime was mounted, you should find the wires there. They should appear dead unless you have someone push the button. Test that and see. Also see what voltage you have present as doorbells come in commonly three different voltages. Then use a relay to act as the doorbell button you want to use with your wireless chime. I really can't see this getting any harder than that. But again, I can't see your system from my computer screen.

 

The original bell was wired however it was battery powered it's always been battery powered by a 9v battery the wires for it had been cut within the door the remaining wires had all been hacked away at so I had to run new ones

 

Blury pic of the original bell lol