You cannot merge two different accounts in Benchling.
If you have two accounts that you would like to combine, you can pick one account that you would like to share all your data with, and send an email to firstname.lastname@example.org to request that the other account be closed.
To share all data from one account with another account, you can open the settings of each of your projects in the first account and share the project with the second account. You can either change the owner of the project to the second account, or you can add the second account as a collaborator (more details here).
You can only share projects with other users on the same domain (e.g. benchling.com). If you have two accounts on different domains (e.g. biotechtx.benchling.com and pharmarx.benchling.com), you must export all data from one account and import it into the other (more details on exporting here).