Rented Makita LS 1011 Manual. cannot move guide to 45 degree angle cut. Have no manual.

you may have tap the saw to move tilt.
The cuttinghead of your compound miter saw can be
tilted to cut any bevel angle from a 90 degree straight
cut off to a 45 degree left bevel angle. Loosen bevel lock
handle (A) Fig. 19, tilt cutting arm (B) to the desired
angle, and tighten lock handle (A)
Delta MS250 Instruction Manual Adjusting Pointer Locking Cuttinghead In...

Distinti gi? check in internet forum the online manuale?

check for slide wear on the mounts
if it has any it allows the motor and saw to drop sideways and alter the cut angle
you can compensate by moving the setting that bit extra and the locking it up

the slide can be angled by the degree plate where the timber sits
the blade can be angled by the degree plate on the arm that mounts the saw
so you can get a 45 degree to the timber length and a 45 degree angle cut to that angle to give you a corner mitre cut

normally they do
they cut at angles across the material
there is also a adjustment at the back of the slide that allows the head to be tilted
there is an angle gauge there and a pointer to give you the tilt angle
by adjusting that and the across the bed angle , you can cut compound angles
set the angle and then test cut as the angle may not always be exact ( setting it on 10 degrees on the scale may be 10 1/2
degrees in reality so testing gets it dead right)
adjust as necessary

Did you check to see if the saw has a locking nut on the front of the bevel gauge handle? Its possible you just locked it into position and forgot to unlock.

I used a power saw every day for years. Makita is a good brand. We used Milwalkee and Craftsman. My Milwalkee, I used the side of my hand to hit it into place >> I didn't hit it real hard, but the angle setting should move a bit sluggish so you can get to the correct cutting degree using one hand while holding saw in other hand. If the angle setting is floppy loose, you have to use two hands to get it set.

The whole guide assembly should come loose from the motor part. Take it apart. Remove the dust & dirt. Spray a bit of WD-40. It should be good to go. Remember the saw is your friend so cut straight and fast.

Up-vote if this helped. Thanks for the feedback.

When using the gauge on your saw it is off on the 45 degree cut? If so you might have to use a tri Square every time you want to cut a 45. Sometimes the lock gauge for the 45 angle may be off some. When you put a tri square on the board you cut it is not a true 45 even though the saw says it is?

loosen the miter lock, tilt the table to 45 deg. tighten the miter lock

Are you having problems with the miter or bevel ? Are you asking how to physically move the saw to that degree angle?