Fixing drywall typically involves repairing holes, cracks, or other damage and there are a number of techniques to solve different types of holes. Here’s a step-by-step guide on how to fix a drywall:

1) You will need the following materials:

• Joint compound, plaster (also known as “mud”)
• Drywall tape
• Utility knife
• Sandpaper (medium and fine grit)
• Putty knife
• Drywall patch or scrap drywall
• Drywall screws
• Screwdriver or drill
• Primer
• Paint

2) Preparation is key, you will need to prepare the damaged area:

• Remove any loose or damaged drywall around the hole or crack.
• Use a utility knife to create clean edges around the damaged area. It helps to cut along straight lines or square shapes.
• If necessary, cut a piece of drywall or use a pre-made drywall patch that fits the size of the hole.

3) Install a drywall patch:

• f you’re using a patch, place it over the damaged area and trace its outline onto the wall.
• Cut along the traced lines with a utility knife to remove the damaged drywall.
• If you’re using a piece of scrap drywall, cut it to fit the hole snugly.

4) Secure the patch (Drywall cut):

Attach the patch or scrap drywall to the wall using drywall screws. Place screws around the edges of the patch, ensuring they sink slightly below the surface.

5) Apply drywall tape:

• Place drywall tape over the seams around the patch or the crack.
• Use a putty knife to smooth out the tape, ensuring it adheres well to the joint compound.

6) Apply joint compound:

• Using a putty knife, apply a thin layer of joint compound over the tape and the patch. Extend the compound beyond the edges of the tape to blend it with the wall.
• Allow the compound to dry completely as per the manufacturer’s instructions.

7) Let it dry, then sand and repeat:

• Once the compound is dry, sand it lightly with medium-grit sandpaper to create a smooth and even surface.
• Apply a second coat of joint compound, extending it slightly beyond the first layer.
• Let it dry and repeat the sanding process.

8) Once flat and dry, smooth and paint:

• Apply a third and final layer of joint compound, feathering it out further to create a seamless transition with the surrounding wall.
• Once the compound is dry, sand it again with fine-grit sandpaper until the surface is smooth.
• Wipe away any dust with a damp cloth.
• Prime the repaired area to ensure even paint absorption.
• Finally, paint the wall to match the surrounding area.

Other options would be to create a wall brace where you stick a backing bit of dry wall through the gap and give yourself a platform to apply another better-sized cut of drywall.

The process may vary depending on the severity of the damage. For extensive damage or if you’re unsure about your abilities, it’s advisable to consult a professional.