How to fix cabin handle

Since you didn't say which door or what's actually wrong with it, start with the symptom — it tells you what to fix before you buy anything:

Handle pulls but the door won't open from inside: the handle itself is usually fine. The cable from the handle to the latch has come off, stretched, or broken, or the latch is the problem. Check whether the door still opens from the outside handle. If it does, the fault is on the inside handle side — cable or handle. If neither handle opens it, suspect the latch itself.

Handle feels loose or floppy, with no resistance: the handle pivot or its cable clip has broken. This is the classic broken-handle case, and a replacement handle is the fix.

Handle won't pull at all / feels stuck: the latch may be seized or the cable kinked or jammed. Don't force it — a stuck handle that gets yanked hard usually snaps, and then you have two problems.

Handle is cracked or snapped off: no diagnosis needed. Replace the handle; just check the cable and its clip while you're in there, since a broken handle often takes the clip with it.

Getting the door panel off without breaking anything. Work with the window up and the door open. The screws are usually hidden behind small trim covers behind the interior handle and in the armrest pull — pop those covers off gently and remove the screws. Then work around the edge of the panel with a plastic trim tool, popping the clips one at a time. Once the clips are free, lift the panel up off the window ledge — don't just pull it straight out, because the top edge hooks over the door frame. Unplug the wiring connectors and unclip the handle cable, and set the panel somewhere flat. If a clip won't pop, stop and look for another hidden screw before forcing it — cracked panel tabs turn a handle job into a panel job.

Swapping the handle. Unclip the cable end from the old handle and remove the handle from the panel. A replacement interior door handle commonly fits your Prius, but always confirm against your vehicle's exact trim and engine and the product's fitment data before buying. Fit the new handle, clip the cable back on exactly the way the old one sat, and make sure the cable isn't kinked or routed over a sharp edge.

Test before you put the panel back. With the panel still off, pull the new handle and watch the latch move — it should release cleanly, and the lock should still work. Only refit the panel once that checks out, then test again from inside and outside with the panel on. If the handle and cable are both good but the door still won't latch or unlatch properly, that's the latch mechanism, not the handle — and if you're not comfortable working on the latch, that's the right point to hand it over. If unsure, consult a professional mechanic.