You can only transfer crypto from your main account into your sub-account. To transfer funds from your sub-account back to your main account, you must do this within the main account.
On the web
Login to your BloFin main account and go to [Transfer] via the following:
1. Click on [User Avatar] -> [Sub-accounts], find the sub-account that you want to transfer funds and select [Transfer].
2. On the Transfer interface, select the [Sub-account] you would like to transfer and your preferred crypto in [Asset].
3. Adjust the [From - To ] details according to your preference.
4. Fill in the [Amount] and click on [Transfer] to complete your crypto transfer from your main account to your sub-account