If you arrive in Cologne main station, please go to the big hall facing the cathedral. Within the train station building go downstairs to the subway, U signs.
There is a ticket counter and a vending machine.
Short distance ticket is 2 Euro and named Kurzstrecke
Get down the second stairway to the train.
Line 5 to Heumarkt
Two stops and you are there.
Leave train, turn left and take the lift to level 0.
The lift ends in front of hotel!
If you escalators end somewhere else and you need to cross the road.
BTW: from Central Station to Dorint Hotel it’s just 1.0 km (10 min +/-) walking.
Depends all on the luggage and how fit you are.
It is mostly pedestrian walkways from the train station to the Dorint Hotel, so dragging a suitcase with wheels is not a problem.
Hohe Strae is the main shopping street. It may be better and faster to walk a parallel street.