How do I merge 2 accounts that appear to have the same name

How do I merge 2 accounts that appear to have the same name

I am evaluating Zoho. I imported about 10k contacts, and then tried to add a new contact for a new individual at a company that was in the original upload. I now have 2 Accounts with the same name.

a) How do I merge them
b) When I create new contacts in the future, how can I select account name from a list of existing account names to avoid recurrence of this problem.