Tenho duas conta no Garmin uma antiga e outra mais nova com emails diferentes , tem como juntar as duas e ficar apenas só com um email ?
Not really. You can export activities and daily data from one account and import them into the other one. Use the "original" format where available:
How Do I Export Data Out of Garmin Connect? | Garmin Customer Support
Import is at https://connect.garmin.com/modern/import-data