You can attach a card with your ad account with the following methods:
1. Ad launcher
2. Ad Manager
Ads Manager
In ads manager, you can simply select the profile, and then you have to go to the Ad accounts option where you will find your ad account. Now you will see an actions button, so you have to click on it and select Attach Card option, and then you have to select the particular card which you want to use in the ad account. Once you select the card you can simply click on attach card option and the card will be attached to your ad account.
Ad Launcher
In the ad launcher, you can simply click on the actions button in the ad account then you have to select attach card option which will open a pop-up, so there you have to choose the card which you want to use in the ad account and then click on Attach card option which will attach your selected card on the ad account.