You must let unRAID do the format of any drive that is part of the array, so removing it isn't what you want to do. If you have already added it, and started the array, then unRAID is probably offering to format it right now, if it hasn't already done so. And it is probably XFS since that it the default for array drives in V6.
If for some reason you have already formatted it to a different filesystem, stop the array, click on the drive to go to its settings page, and change the format. Then unRAID will format it when you start the array.
Not only does unRAID have to format any drive it will use, but formatting a drive (a fairly quick operation, since it is just writing a small amount of metadata that represents the empty filesystem) that is already in the array will also update parity, so no parity sync is required.