What to do after dirt bike riding?

Wash your bike after every ride.

Be gentle. We recommend simply using a bucket of water and a selection of brushes to knock off mud. You can use a pressure washer, but be careful to deflect the water away from the bike, so you don't force water and dirt into areas where it can damage engine or electrical components.

You've asked this lots of times on Y!A. This is the cycling section where we use pedal power not petroleum of "gas".

SIRDAR S-900 27 Speed 27.5 inch Mountain Bike Aluminum Alloy and High Carbon Steel with 2 Replaceable Seat, Full Suspension Disc Brake Outdoor Bikes for Men Women: https://youtu.be/I_CnzEG8C1k

You wouldn't have to do that if you bought MTB.  You want the 'Motorcycle' section, not the 'Cycling' section.  Find it here.  All Categories - Cars & Transportation - Motorcycles  https://answers.yahoo.com/dir/index?sid=396546040  

In the Cycling section, this is a 'dirt bike'.

i would ask a mechanic about it

You do realize you posted in the Cycling section where questions are answered about bicycles. You relied on YA to post the question for you instead of doing it yourself. Use the edit icon to move your question to the Sports>>Motorcycle Racing section.