I didn't find a guide for the SM-A136U, but the Spanish site Nadie Me Llama Gallina has one for the SM-A137. Given they both fall under the A13 model number, I suspect there won't be much difference between them. Anyway, here's how to replace that fingerprint sensor/power button.
Manuals / Samsung Galaxy A13 SM-A137 / Fingerprint and Power Sensor Flex Cable - Nobody Calls Me Chicken
As you might guess, the site is written in Spanish, but if you use it with a browser that includes a translator like Chrome, the guide works just fine no matter what your native language is.
P.S., A little research shows the A137 is a 4G phone, while your A136U is the 5G model. I still maintain there shouldn't be major differences in the procedure between the two.
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I had to replace mine and after dropping the phone a few times had issues with it again. Take Sim card slot out and open carefully (ribbon cable is attached from button to board). Take out screws of top plastic piece and gently pry up the clips on side. There is a little metal piece that sits over where the ribbon cable attaches to the board. I have had to pull that out and slightly bend it inwards because the cable wasn't making good connection after dropping it a couple of times. After I did that it worked fine for quite a while. I still have to replace the power button again though because it finally failed. Hop this helps.
crwdns2934271:0crwdnd2934271:0 Joe Welch crwdne2934271:0