welcome to healthcare magic forum
thank you for your query
yes,there is relation between vitamin b 12 and skin problem .
low b12 cause hyper-pigmentation and skin thickening ,but there are also other reason for this like heredity ,smoking ,sun exposure ,acanthosis
nigrecans etc .
you can get b12 injection
for 5 times to restore it .
sunscreen and good moisturizer are corner stone for treatment
level will also advise to rule out it resistance .
so best thing is consult dermatologist
and make treatment plan and follow it
i hope i answered your question