Some code readers (and presumably Testbook is one of those) will let you set / unset the light separately from any code activity. I need to dig back and find the software for my reader and go have a look at my RR in a bit, can't even remember the name of what I use now.
On my 1991 RR Classic, disconnect battery for short while (~10-30 seconds) will reset "Check Engine" light.
BTW, Service Engine light emission service reminder (I think every 57K miles). On 1991, it's reset is under passenger seat in small brown box near relays. Remove label covering hole, insert something to reset.
When the problem has been repaired the computer will automatically turn the check engine light off. I have been told by a LandRover mechanic that after a certain amount of cycles it will turn off. I had MAF code and the check engine light came on, I fixed problem and light turned off.