First, fill out the Application for Accepting payments online (see here for Estonian, Latvian and Lithuanian versions). The bank will contact you as soon as possible, not later than on the third business day.
Log in with your Swedbank business account, navigate to Bank Link Portal (EE, LV and LT) and find the Keypair Generator tab. As per instructions in that tab, the keys generated here are not accessible to the bank. Click Generate keypair button and save the keys in a file via the provided buttons.
NB! Once you have generated and downloaded the keys you must send the Public key text file to your customer manager or to firstname.lastname@example.org (EE), email@example.com (LV), firstname.lastname@example.org (LT). This is required to finalise the agreement.
Select the Add button for Swedbank and paste the Merchant ID to the fields in the first field on the left. Select your country (EE/ LV/ LT) and copy the Public key and Private key from your downloaded text files into the according fields.