"把搁在支架上" can be translated as "place it on the stand/bracket" or "put it on the support/rack" depending on the specific context and the type of stand or support being referred to.
If it's a general stand or bracket for holding something, "place it on the stand/bracket" would be appropriate.
If it's a more specific support or rack, such as a music stand, a camera tripod, or a shelf, you could use "put it on the music stand," "set it up on the camera tripod," or "place it on the shelf," respectively.
In the most general sense, "place it on the stand" is a common and versatile expression.