I messed up my model - how to get right angles back?

Kia ora everybody,
this being my first post and also being rather new to 3d-modelling, apologies in advance if I don’t get the lingo right.

The image is part of a larger model. The basis was something i crudely drew up in F360 and then refined using Blender 2.90.1. The refining went surprisingly well, but on final inspection I discovered this bulge in a formerly rectangular box shaped hollow in the model. This is supposed to house a different print, hence it should preferably be back to it’s original shape.

I tried the usual approach of trawling the web, but most likely due to me not knowing the appropriate keywords, I couldn’t come up with anything helpful.

Thanks in advance for any help.

Select the edge then press s then z then 0 to align them horizontally. Use the transform operator in the N panel to position the edge where you want on the x or y axis.

Do I just select the part of the edge that is out of alignment or the whole edge that I want straight?

1)Select the edge you need to straighten

  1. Press S then Z then 0 to align them horizontally (press the keys one after the other, not all at once)

  2. Copy the Z value of an edge that is already properly aligned (in the sidebar - press N)

  3. Select the misaligned edge and paste the Z value.

Now everything should be aligned. In this case, I dont know if the global or local values make any difference.

If you want to flatten a surface, you can also use the “LoopTools” addons that ships with Blender.
Select all the faces you want to flatten then right click:

Repeat steps 3 and 4 above to align them with the rest.

By the looks of things, it looks like the bulge is “popping” out on two axis, so you might have to try both the Z (up and down) and X (left to right).

Thanks so much guys!

Took me a while to work through all the bulged triangles, but in the end the box is again appropriately box shaped. I had to go through multiple iterations of the process but it worked.

I would delete the part and model it back, but it depends what workflow suits you. Just because iam not confident to make lots of iterations. I would connects the edges to keep exact corner and then connect the rest to the edge.

and this is just the fast way where I didnt care about topology and just pressed F (or alt+F if you really dont care) to filling the space between edges.