So how can I be able to do that with trust wallet? Because am changing it to a self custodian wallet which is electrum.
I think it will be better to wait for Hhampuz instructions as regarding the change of wallet.
However, for the purpose of learning signing a message from Trustwallet is not possible because it doesn't support the feature but you can import the wallet to anyone that supports signing a message as long as you have the keys to the address. First of all, select the wallet with your old address which is the one you will sign message from. Then, click on the menu option with three dots and select sign/verify message option and you'll see a blank field where you write your message. After you have written your message, click on sign message icon at the button and approve the message by entering your password. This process is for Bluewallet and I think it will be the same with electrum too.
Edit: You have nothing to bother, I just checked the Spreadsheet and your address is already changed to the new one. Cheers 🥂