It isn't tubeless so you need to fit a new tube. Take the wheel off, remove tyre or pay a shop to do it.
How old is that tyre? Check date code, you may need something newer which will be safer and give better grip
To remove wheel, remove axle nut, remove nut on brake torque arm, remove brake adjuster nut and push down on brake pedal to remove rod. Don't loose the barrel in operating arm (do not remove operating arm)
Pull axle, drop wheel, roll it forward and unhook drive chain. Roll wheel out to rear. You only need a few tools to remove wheel, socket for axle nut and 12~14mm for torque arm (should be 12mm but could have been changed in 35+ yrs)