Some issues can be resolved using trenches plumbing technology, but this specific problem of an old underground 90, mixed with tampons/blue shop towels/grease cannot be fixed like that. That fitting needs to be dug up, replaced with a longsweep, with and added 2 way cleanout that is jetted once a year both ways, with an investigation on who is flushing the towels, because that’s who I’d be backcharging the costs too