Remove 1 disk from 3-way raid1

Hi, I have an SP32 with 3x4TB.
Right now it is configured as a 3-way Raid1 but would like to take 1 disk out and format it while keeping the raid1 with 2 disks and data unaltered.
How should I proceed?
Many Thanks

# df
Filesystem 1K-blocks Used Available Use% Mounted on
/dev/md2 100659568 4449656 91073584 5% /
devtmpfs 16216488 0 16216488 0% /dev
tmpfs 16229376 0 16229376 0% /dev/shm
tmpfs 16229376 17584 16211792 1% /run
tmpfs 16229376 0 16229376 0% /sys/fs/cgroup
/dev/sda1 522228 2664 519564 1% /boot/efi
/dev/md3 3743751816 1458309504 2095247628 42% /var
tmpfs 3245876 0 3245876 0% /run/user/0
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# fdisk -l
WARNING: fdisk GPT support is currently new, and therefore in an experimental phase. Use at your own discretion.

Disk /dev/sda: 4000.8 GB, 4000787030016 bytes, 7814037168 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk label type: gpt
Disk identifier: 7BFDBF5F-5302-412C-BCBD-0EED3512C033


# Start End Size Type Name
1 2048 1048575 511M EFI System primary
2 1048576 205846527 97.7G Linux RAID primary
3 205846528 7812978687 3.6T Linux RAID primary
4 7812978688 7814025215 511M Linux swap primary
WARNING: fdisk GPT support is currently new, and therefore in an experimental phase. Use at your own discretion.

Disk /dev/sdc: 4000.8 GB, 4000787030016 bytes, 7814037168 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk label type: gpt
Disk identifier: 6A4F29A5-5228-4A4B-9D77-784028F2AB76


# Start End Size Type Name
1 2048 1048575 511M EFI System primary
2 1048576 205846527 97.7G Linux RAID primary
3 205846528 7812978687 3.6T Linux RAID primary
4 7812978688 7814025215 511M Linux swap primary
WARNING: fdisk GPT support is currently new, and therefore in an experimental phase. Use at your own discretion.

Disk /dev/sdb: 4000.8 GB, 4000787030016 bytes, 7814037168 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk label type: gpt
Disk identifier: AB85EBB3-92DE-4125-8E43-FEC6A8A82559


# Start End Size Type Name
1 2048 1048575 511M EFI System primary
2 1048576 205846527 97.7G Linux RAID primary
3 205846528 7812978687 3.6T Linux RAID primary
4 7812978688 7814025215 511M Linux swap primary

Disk /dev/md2: 104.9 GB, 104856485888 bytes, 204797824 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes


Disk /dev/md3: 3894.9 GB, 3894851600384 bytes, 7607132032 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
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