Add single flute engraving bit

How do you add Single Flute Engraving Bit in Easel, what are the steps?

You can’t add bits to Easel.

But you can edit the bit diameter under “Other”

Are you talking about single flute spiral/straight bit or engraving bit. I don’t know any single flute engraving bits if there is any. They are all similar to V carving bits, some have replaceable blade, those are only one side cutting edge.
In that case you can’t change angle but you can double the speed because of single cutting edge versus double.
Same thing applies to single flute spiral or straight bits. All you have to do is increase your spindle RPM.
When ever I use single flute 1/8" spiral bit for wood I use Dewalt Speed 2, for acrylic cut I use Dewalt speed 1.