To add a contact in your TronWallet app, first tap on the third icon from the left on your navigation tab bar (the one that looks like an address book) to go to Address Book. There, you will find two tabs: Contacts and Accounts. Your Contacts tab should already be active. There, if this is a new wallet, you will see an empty contacts screen. Tap on the floating button at the bottom that says ADD CONTACT. This will take you to the create contact form where you will be asked to provide a name as well as the address of the contact. Once you have decided on a name you will have to input the address. Here you have 3 choices. You can either type the address, tap on the Scan button (the rightmost icon) or you can paste an address that is already in your clipboard. To look for an address to paste, tap on the button with two vertical arrows going opposite ways on your navigation tab bar to be taken to the Transaction List Screen.
In the Transactions List Screen, tap on the transfer transaction you want the address of and a modal will open with the following options: Add Contact and Copy Address. Tapping on Add Contact will automatically redirect you to the add contact form with the address already filled in, but to demonstrate the paste button, tap on Copy Address and go back to your Address Book Screen. The form will still be showing with the name already filled in. Then, Tap on the clipboard icon to paste the address and proceed by tapping on the ADD Button. You should now see your Contact listed in the Contacts tab of your Address Book Screen.