First make sure that LTI is enabled for your school or district organization by contacting ThingLink here. 

Log into your Canvas Admin account, select Admin from the left menu, and click on the Site Admin link. 

In Site Admin, choose Settings on the left, then click the Apps tab and use the blue button to add an App. 

Next you can add your ThingLink LTI information to link your accounts. Refer to the following list for relevant information:

Configuration Type: By URL

Name: ThingLink

Consumer Key: Your ThingLink OAuth Consumer Key

Shared Secret: Your ThingLink OAuth Secret

Config URL: https://www.thinglink.com/auth/lti/confi

After clicking Submit the ThingLink app will be configured and you can link to it through course modules.