how to re-install TWRP from Linux?
The quoted text is for "uninstalling" TWRP  

If i understand your question correctly, your only concern is to update TWRP to newer version  

before flashing new image it is recommended to test if it works without flashing (not all devices support this)  

fastboot boot twrp.img


installing TWRP depends on device  

some devices don't have recovery partition. in this case you need another self installing zip file which will install TWRP in recovery-ramdisk in boot partition  

if device has separate recovery partition you can simply flash the partition image  

this can be done from fastboot  

fastboot flash recovery twrp.img


from pc command line  

adb push twrp.img /dev/block/bootdevice/by-name/recovery


or even from TWRP itself in Advanced - Terminal  

cat /external_sd/twrp.img &gt; /dev/block/bootdevice/by-name/recovery


Some TWRP variant does allow backup/restore recovery. in this case you can just rename the twrp.img into recovery.emmc.win, place it into empty backup folder TWRP/BACKUPS/*/recovery and restore backup  

Note: Your bootloader must remain unlocked as long as TWRP (or any other modified partition) is installed. re-locking bootloader is only recommended after you flashed full stock ROM including stock recovery. Otherwise you will brick