UK Noob

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Hi I am new to this and new to fitness. Im 31 and 100kg, the doc wants me to.be under 90kg for my BMI and to help with my snoring, (I want to stop snoring so my gf can sleep beside me again, thats my motivation)

I am aiming to lose 10kg in 6 weeks or so, im on a ship so kinda restricted diet and exercise.wise but there is a gym, how do-able is this?

All tips appreciated!