Make apple alias the Primary Apple ID

See the article https://support.apple.com/en-us/HT202667

On your Apple ID account page

1. Go to appleid.apple.com and sign in.
2. In the Account section, click Edit.
3. Under your Apple ID, click Change Apple ID. If you try to change your Apple ID to an @icloud.com email address created within the last 30 days, you might be asked to try again later.
4. Enter the Apple ID that you want to use.
5. Click Continue.

If you enter an email address that's already an alias or alternate Apple ID, and it ends with with @icloud.com, @me.com, or @mac.com, you see a message to confirm. 

If you mean an email alias - an additional address (which therefore has a different text before the '@' from that of the address you created when you first opened the account) you cannot make this into an Apple ID.

If your original iCloud address also has @me.com or @mac.com versions (with the same text before the '@') as a result of your having been a member of MobileMe or DotMac, Apple confusingly also refers to these as 'aliases' and as they are in effect the same address you can already sign in with any of them. From your description this seems not to apply.