If you wish to add ANY trustlines, you can do so by tapping on the Account tab, see image below:
Tap Wallet & security, as in the image below:
Next click on Assets trustlines, see below:
On the next screen you can see your active trustlines (and revoke them if needed).
To add a new trustline press the "+" button on the top right, see below:
In the next screen enter Asset Code and Asset Issuer, see below:
Be very careful when adding a new trustline, always double-check the data you enter and make sure that the data you have actually matches the token you want to add.
Below is the data to insert to add Stellar CANNACOIN:
ASSET CODE: CANNACOIN