You have not provided any details about the program you are using. I can only guess you mean outlook. If so, close outlook and go to the control panel and open the mail icon, (switch control panel to classic view if necessary). Go to show profiles, change the selection to “always prompt for a profile”. Open outlook again and you will be prompted for your profile choice. Click “new” and create a new profile just for your personal email, naming it differently than the other profile. Then when you want to send as your personal email account open outlook in that profile.
If you are using Outlook go to Control panel -> Mail. Setup a second Outlook Profile and make sure that it prompts you for which profile you want.
Or if you;re using outlook, yu can go to tools/ email account/ add and you can add a pop or IMAP that way both account are on the same profile.