sfdcfox's answer about needing it to be a rich-text field is correct.
If you do change the field type though, your trigger would still not work for two reasons:
- The value you're setting for the
href attribute is not contained in double quotes
- You're not checking to see if
Location is already a link (any subsequent edit would make your Location be
<a href=<a href=some.link>>)
While you could do this with a trigger, I don't think it's the right tool for the job here. At least not with the information you've given us so far. A workflow rule to set to fire only when the record changes to subsequently meet the criteria (with the criteria being that Location does not contain
<a href=) and a field update could take care of this just fine.
You should also be able to create a before save record-triggered flow to accomplish the same thing as a workflow + field update (but it runs a little faster and because it's before-save, doesn't cause before/after update triggers to run again).