Did you take the oil pump off? If so, you can use a punch or screwdriver and pound the seal out and use the old seal to drive the new on in or a block of wood. If you have not pulled the oil pump, you could try to put a screwdriver into the seal and pry it out. I have had good luck with drilling a small hole and putting a screw into the seal and pull it out with vise-grips.
HTH
Jeff

It's all good!
83 Shortbed stepside lots of mods
82 Shortbed fully restored
85 Shortbed daily driver
88 4-runner-Wife's daily driver