You need to do next steps to create additional Administrator Accounts.
At first we need to create account and only after it you can add this account to the Administrator Group role:

1. Navigate to Computer Management. This can be done by clicking Start > Computer Management or via Start > Run > compmgmt.msc

2. In the left hand pane expand Local Users and Groups

3. Right click Users > New User...

4. In the window which pops up, provide the new account a username and a description. Be sure set a strong and secure password for the account. You may configure the rest of the options as is needed.

5. Once complete click Create.

Next step will be adding your new account to it into the Administrator Role. Please do next actions:

1. On the left hand pane of Computer Management, expand Local Users and Groups and click the Groups folder.

2. Double click Administrators from the middle pane.

3. In the popup window, click Add...

4. In the new window which opens, select Locations then select the top most item in the list which will be your local server and hit OK. If you are prompted for a password at this step click cancel.

5. Once the Location has changed enter your new users Username in the objects box then click Check Names to ensure its valid. Once Windows has validated the account, click OK.

After it your new account will be setuped and ready for use.