To enter Recovery Modus (RCM) you need to short pin 1 and 10 (in the right joy con rail). The safest way is to use a 3D printed jig or a paperclip.
BE CAREFUL! There is a chance that you will irreparably damage the right joycon rail. So always be as careful as possible!
Using a 3D Printer
If you have access to a 3D Printer you can print the model by following Fail0verflow’s guide here.
Simply slide down the jig in the right joy con rail and press power + volume up key to enter Recovery Mode.
Using a paperclip
You can bend a paperclip to make contact between pin 1 and pin 10. This is probably the cheapest and easiest method.
The following tutorial is based on the work of GBATemp user unvalueblespace and shows you one of the many possible ways create an RCM Jig and start the console in Recovery Mode. These DIY steps can cause damage to your console, so proceed with caution. We are not responsible for damages.
The intention is to cut and bend the paperclip so that it touches the pins on the inside of the right joycon rail. Please note that the clip needs to have the exact size so that it touches pin 1 and pin 10.
After connecting the paperclip to the console you can boot in Recovery Mode by pressing the on / off button and the volume up button simultaneously. If the screen remains black you have successfully booted in RCM. When the Nintendo logo appears, try again and make sure that pin 1 and 10 are touched by the paperclip.
Using a cable
You can use a cable to bridge the connection between pin 1 and pin 10. This method is shown in the video below at around 1:42.
After connecting the cable to the console you can boot in Recovery Mode by pressing the on / off button and the volume up button simultaneously. If the screen remains black you have successfully booted in RCM. When the Nintendo logo appears, try again and make sure that pin 10 and a ground is touched.