I’ll attempt this, let me know if this is helpful or not.
So on the keycap that you removed there’s typically two different types of attachment: hooks and clips.
What you need to do to attach the keycap properly is first slide the keycap to attach the hooks, then press it to attach the clips.
If the hooks are at the top side of the keycap, then you put the keycap slightly higher than it would normally sit attached on the keyboard and slide it downward while slighly pressing on the top side of the keycap. Then you press with a bit more force on the lower part of the keycap until you perceive a click from the clips attaching.
The typical mistake is to try to press the hooks as if they are clips - just straight down. This would likely cause the hooks to be damaged irrepairably and the key not able to be attached fully back. (In my experience.)