XIAO BLE Sense (nRF52840) not able to upload

I can not find my device above regularly in the arduino IDE. I can only upload code through bootloader which means I can not use the serial monitor, and I keep getting errors in my ide. Also the arduino ide keeps mistaking by sense for just a regular nRF52840. I have the .json file in my prefernces and I downloaded both board packages. Right now to change it to sense I am using Tools > Board: > Seeed nRF52 mbed-enabled Boards > Seeed XIAO BLE sense - nRF52840. Does anyone have any advice to fix this or atleast instructions to burn the bootloader? I have an extra arduino uno. Also before, when I could see the port normally, it was on com 7, and then once enterng bootloader it went to com port 9; but now I cant see 7 altogether meaning my arduino ide does not recognise the XIAO BLE sense normally, it only detects it in bootloader mode which brings the issue of not being able to use the serial monitor.

Did you have a good weekend?

**1.**First of all, you need to carefully distinguish the model of your board and choose the right board library (although the difference between sense and no-sense is not big, it is still recommended to use the right board library).

2. The reason for the change of serial port, by com7->com9, is that the problem of its size limitation leads to the lack of some corresponding USB chips inside, and this problem does not affect normal use.

3. As for the problem of not being able to use the serial port monitor is the most critical, you may need to re-burn the firmware to restore it, which can be solved (the failure to recognize the serial port is because some wrong burning problems cause boot to be destroyed, so you need to manually enter the boot mode to burn, this problem is a big problem for xiao, Because it is usually used for wearable low-power small devices, there is no integrated TTL to USB chip, which can not solve the problem in the short term.

I hope it can help you. I wish you a happy life.

I have an Arduino uno at home can you help me figure out how to burn the bootloader via the uno?

Perhaps this “Burn boot loaders to Arduino UNO” Wiki can inspire you and help you:
Atmel AVRISP STK500 USB ISP Programmer | Seeed Studio Wiki


if I am going to reflash, I need a j-link device but they are very expensive, so what do you recommend

I think SEGGER’s J-link product is a good choice