With a standard tank band, you loosen the buckle a bit, slide it down the tank and then tighten it and snap it in-place. Make sure the band is wet first, so it is stretched when you tighten it before the dive.
I am partial to bands that open all the up so you can put the BC on the tank from the side, instead of having to slide the band BC over the top of the tank. My favorite is the ScubaPro style, SP charges a ton for their gear so I get mine from Dive Rite Express, for around $20/each right now on sale for $16 each.
If you go this route, you might need to check that the Zeagle BC can take this style of band.
Over the years I have my entire family's tank straps to these....they are easy to use and don't slip.
Hope it helps.....M