How do you change the headlight bulb (low beam) on the passenger side of a 2000 toyota celica?

Sounds like you need to look for a bad ground for the passenger headlight.

ck connector for bad contact and power, if no power headlight switch may be fault would have to trace system for voltage .

there should be separate relays for your headlights inside the fuse panel under the hood drivers side fender

Sorry, this is one of those you have to feel for the socket to remove it. did you check the fuse, it is rare that both low beam bulbs would go out at the same time. Don't remove the front bumper what ever you do, it is a nightmare and an accidental deployment of the airbag could occur.

y need new bulb on the passenger side and inst. cluster need to be checked for fuse or bulbs replacement.

The passenger side has plastic firewall covering the area you need to get into. If you pop the hood, and remove the plastic covering the components on the passenger side (the same chunk that covers the receptacle for the anti-freeze) you should be good to go. After that bit, it is exactly the same as changing out the driver's side light.

The globes filament for low beam are most likely both blown . Check if the plug is getting voltage when the low beam is on or buy a replacement globe and check if this is the case.
How do you know both low beams stopped at the same time ?
They most likely blown at different times but you notice it when both go out and you have zero light. Had this happen to me on a ford falcon EA . Was the globes.
Try not to handle the glass on the replacement globes if Halcyon globes .

The adjustment screws/nuts should be located either on the top of the headlamp assembly, behind the headlamp assembly, or near the frame rail by the radiator support.

You will have vertical adjustment screws for each independent beam (separate highs and separate lows, but will be same screw if highs and lows are the same bulb). You may also have additional horizontal adjustment screws as well

Park your car on a level ground 30 feet from a wall and measure the height from the ground to the bulb and mark on a wall (do this for highs beams and low beams if the bulbs are separate, if highs and lows are the same bulb, only do it for the lows)

For Low Beams: If the headlights read VOR, then aim the brightest part or cutoff part just below the mark on the wall. If it says VOL or nothing, aim them 2 inches below the mark on the wall.

For High Beams (if separate from low beams): Aim the headlight directly at the line you marked on the wall.

The adjustment screws/nuts should be located either on the top of the headlamp assembly, behind the headlamp assembly, or near the frame rail by the radiator support.

You will have vertical adjustment screws for each independent beam (separate highs and separate lows, but will be same screw if highs and lows are the same bulb). You may also have additional horizontal adjustment screws as well

Park your car on a level ground 30 feet from a wall and measure the height from the ground to the bulb and mark on a wall (do this for highs beams and low beams if the bulbs are separate, if highs and lows are the same bulb, only do it for the lows)

For Low Beams: If the headlights read VOR, then aim the brightest part or cutoff part just below the mark on the wall. If it says VOL or nothing, aim them 2 inches below the mark on the wall.

For High Beams (if separate from low beams): Aim the headlight directly at the line you marked on the wall.

Remove the plastic cover. No need to remove the assembly.