What technique is used to remove the bubbles and big hole from swiss rolls?
Pouring your icing over the roll is the easiest method, but only covers the top and sides, but not under the curve.  This is a common and traditional treatment.

Place the roll (seam side down) on a wire rack over a sheet tray, and pour the coating over.  The sheet tray catches the run off so that you can reuse it.  

This can be done with ganache, tempered chocolate, or a sugar-chocolate based glaze.  No matter which glaze you use, you want it thick enough to adhere to the roll quickly.   Let chocolate or ganache cool until they are fairly thick and coat a spoon well.  

After you pour, pop any bubbles which may appear with a toothpick or the tip of a pointed paring knife.

This video from Zoe Bakes shows the basic technique using ganache, although it is on a standard round layer cake rather than a Swiss roll.



Getting coating over the entire surface of the roll (including the bottom side) is much more challenging.  It is best done by dipping, if the Swiss roll is not too large.  You will need a coating that will set up hard, either tempered chocolate or sugar-based glaze.  This will also require a great deal of surplus glaze, although it can be reused.

If the roll is too large to feasibly dip, you can still do the pouring method.  Start with the roll bottom side up, pour the coating and let it set, then turn it top side up and do a second pour.   This will leave a seam, which is hard to avoid if you cannot dip.

You will get better results by freezing the roll first with either technique.

See related:
Ganache coating on a roulade