There are several ways to get a bounding box; the standard-cell ID layer (in the GDS) is one of them. Otherwise, if the GDS has no bounding-box information, then you can declare it by hand by putting the cursor box where you want the abutment bounding box to go, typing "box values" to get the values (in internal units), and then plugging those values into the command

property FIXED_BBOX "<values>"