Where you store your bitcoin? In wallet or in exchange wallet?
You should be your own bank with non-custodial wallets:
Bitcoin Core or
Electrum wallet. Bitcoin Core full node requires huge space in disk, if you don't have much but want to use Bitcoin Core, use prune node. Electrum has app for Android (get link to download the app from the link, don't search Electrum on Google Play)
You can check and turn on change address in your wallet, Replace by fee.
In Electrum, if you want to send bitcoin from address A (in Address tab, choose Address A and right click to choose Spend from).
Click on Send tab to fill in the address of receiver.
Click on amount (can choose Max amount from address A or any amount you want to send)
Click on Pay: You will see the message box, see in Fee rate: default is ETA that is high fee usually. You could change it to mempool. The fee now is high so the lowest fee you can use fee for 10 MB from tip with the fee is 6 sat/byte.
If you accept that fee, enter password, click on Send: You will see details for the transaction (amount send, fee)
If you see things are ok, click on Broadcast, Finalize, and that amount will be sent.
But what happens if the transaction is smaller than the amount present on an address?
You can not send more than the amount you have.
But you can click on 2 or 3 or multiple address in one wallet to spend it. Right click > Spend from and do same steps.