Loose crank exercise bike
You need to figure out what's wobbling.  The pictures I find suggest that it has a three-piece crank, so you can get wobble from three sources:


The pedals are wobbling where they screw into the crank arms.
The crank arms are loose on the crank shaft.
The crank shaft is loose in its bearings (or the bearing cartridge is loose between the "cups'.


The "fix" is to tighten whatever is loose.  So very carefully examine:


Hold one crank arm and try to wobble the pedal screwed into that arm.  Repeat on the other side.  You should not detect any looseness (save for a small amount in the pedal bearings).  If you do detect looseness, use a wrench to tighten the pedal shaft into the crank arm -- clockwise on the right side, counter-clockwise on the left side.
Hold one crank arm and try to wobble the other arm.  Try to detect looseness in the connections between the arms and the shaft running between them.  If you detect such looseness you need to tighten the bolts that hold the arms to the shaft.  This is generally a right-hand thread on both sides.
If you detect no looseness when you wobble one crank arm while holding the other steady, but the whole assembly of crank arms and shaft seem to rattle as a unit, then the cups holding the crank bearing need to be tightened.  I'm thinking the right cup uses a left-hand thread and vice-versa, but I don't recall for sure.  And if there are loose bearings for the crank shaft, vs a "cartridge" of shaft and bearings together, then you need to use some care to get everything just "tight enough", without over-tightening.


Of these possibilities, #2 is the worst, as riding with your crank arms loose very quickly damages the arms to where they will no longer fit tightly.