If you downgrade to 2.1.0 on a 2DS or New 3DS and left Wireless Communication off, you can re-enable the wireless by removing the battery for several seconds then booting back up.
If you've been using the New 3DS's microSD Management to transfer files to your SD card, this will no longer work on 2.1.0, make sure to have a microSD card reader on hand before proceeding.
Your device may not show your installed games after the ctrtransfer. This is due to the tickets being removed by the transfer, which is why you back them up. They will be restored at the end of the guide.
Never update a New 3DS running 2.1.0 (an Old 3DS firmware) or you will BRICK! You MUST restore a NAND backup or ctrtransfer back to standard New 3DS firmware first!
In this section, we will be flashing your console's [CTRNAND](https://www.3dbrew.org/wiki/Flash_Filesystem#CTR_partition) partition to 2.1.0 in order to take advantage of an oversight in 2.1.0 for the purpose of extracting the [OTP](otp-info) unique to your console. This OTP file is required to install arm9loaderhax, and **cannot** be shared with other consoles.
This is accomplished by [installing a premade ctrtransfer image](https://www.reddit.com/r/3dshacks/comments/4zhe4a/) containing 2.1.0, copying your console specific files (such as `moveable.sed` and `SecureInfo_A`) to it, then fixing the title databases.
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4. Go to "SysNAND Options", then "CTRNAND Transfer", then "Auto CTRNAND Transfer"
5. Select the 2.1.0 ctrtransfer image when prompted by pressing (A)
6. If you do not already have a NAND backup, **backup SysNAND to `NANDmin.bin` when prompted by pressing (A)**
7. Allow the transfer process to proceed automatically, this may take some time
8. Once the transfer is complete, press (B) to go back
9. Press (Select) to eject your SD card
9. Delete the 2.1.0 ctrtransfer image `.bin` and `.bin.sha` from the `/files9/` folder on your SD card
19. Clear Home Menu's extdata by navigating to the following folder on your SD card: `/Nintendo 3DS/(32 Character ID)/(32 Character ID)/extdata/00000000/`