As you manually add new tokens to your Temple account, you provide the following information about these tokens: Name, Symbol, Decimals. Sometimes, when someone send you tokens that have lack of Metadata you will see ??? instead of a Symbol.
If you want to change this info, you need to follow a simple procedure. It's applicable for NFT also.
How it is done
1. Choose the token that you plan to edit:
2. Save the contract address of this token (Click "About Tab"):
3. Return to the main page and choose "Manage":
4. Click Add token:
5. Add updated Details about your token. Use the address of the contract that you have saved on the stage 2.
1. Your Token type. For NFT it's always FA2
2. Add your token address (see p.2 fo this tutorial)
3. Token id, in most cases it's 0
4. Change the Token symbol
5. Change the Token name
6. Change the Decimals number
Also, you may change an image url
Click "Add Token"
6. Return to the main page. You will see the new Token Details.