Is it possible to change background cantrips?

I have an artificer who has the House Cannith Heir background.  This gives me 2 instances of Mending.  After talking to my DM he said its fine to switch one out with a different cantrip.  I can't figure out how to do this on my character sheet.  I can't even select an additional cantrip because artificier only allows 2 at my current level.  Is there a way to change this or do I just need to write it down and remember?

It's not possible to do that directly on the D&D Beyond character builder, unfortunately, because technically it's not allowed by the official rules. (It's a perfectly reasonable house rule, but D&D Beyond is not great at handling those.)

You could create a homebrew feat that grants the spell, and add it via the Manage Feats button on the character sheet (which allows adding feats outside of the normal level progression).

I didn't even think of making a homebrew feat.  I'll do that, thanks!

Quote from Legendary_Jagoff >>

I have an artificer who has the House Cannith Heir background.  This gives me 2 instances of Mending.  After talking to my DM he said its fine to switch one out with a different cantrip.  I can't figure out how to do this on my character sheet.  I can't even select an additional cantrip because artificier only allows 2 at my current level.  Is there a way to change this or do I just need to write it down and remember?

 Neither instance of Mending (from Tinker’s Magic or from your background) should count towards the two cantrips you can choose as an Artificer. 

That's not what they're saying.

The issue is that normally, you'd get four Cantrips in total - one from that Background which is mandated, one from being an Artificer which is mandated, then two from normal Artificer spell progression which are choices. Since the Artificer and Background mandated ones are identical (Mending), they're essentially losing out on a Cantrip.

The DM approved them changing one of the instances of Mending so they don't lose out, but DDB is rigid on insisting they only select the two Cantrips as per normal spell progression. Hence the workaround to add a Cantrip.