pictures would be a great help here,if you have removed the valve,collets and spring the seal will be next in line,simple push fit on/off , your not confusing seals with guides are you.....have a go at resizing the piccies and we can get you sorted
wemoto are still trading, use them a lot without any problems,the way things are at the moment i would be surprised if you get them before we have beaten the virus...wemoto....£2.68 each, part number AA4423, same part for exhaust and inlet valves
Pull them off with a pliars , push on the new ones by hand, and as Bandit says, apply some engine oil to the seal inner and the top of the valve guide. Prior to pushing in the valve ensure the area of the valve where the collet locates is perfectly smooth and also the top of the stem. They can, but not always have burrs on them from use.