Click o to open the Options window, then select UI menu, next set Corpse Targeting value.

You must have a skill that uses a corpse on your bar to be able to target them.
Hold down A by default.
| Skill gem | Required Level |
|---|---|
| 28 | |
| 16 | |
| 4 | |
| 10 | |
| 4 | |
| 12 | |
| 10 | |
| 12 | |
| 12 | |
| 12 | |
| 4 | |
| 24 | |
| 12 |