I accidentally created a second account because I had forgotten about my first account, but now I want to merge them and keep single account.
I want this account to be merged into https://askubuntu.com/users/109523/tobson
Click the Contact Us link at the bottom of this page.
In the link that opens up, click on Merge user profiles under Account Management.
If you have access to both the accounts (ie; you know the Login ID and Password), you can merge the accounts yourself by following the instructions on that page.
Otherwise, you may fill out this form, to request the merger of the two accounts.