Some users will upload multiple attributes that have somewhat of the same meaning. Use the Merge action to bring two attributes into one.
For example, let's say you have attributes "plan" and "plan_type", and you only meant to persist one of these two attributes. First you'll want to choose which of the two attributes you want to keep. We'll keep "plan".
Because we want to keep "plan" we will go find "plan_type" in our attribute management table. If you have a lot of attributes you might want to use the handy dandy search bar.
Once the merge window pops up, you will select the "plan" attribute and click the Merge button. This will merge "plan_type" into "plan".
If a contact already had a plan assigned to them, they will retain that plan. If the contact previously only had a "plan_type", they will now have a plan with the previous "plan_type" value.