how to write a formal letter when taking over new duity/post

Dear All,

Can any one help me to write a formal letter rgading below:

next week i am going to assign my duties in our site office as per HR request(Currently i am working in main office) i want to reply to HR e-mail that sould be contain “taking over my new duties & need to thank for main office director/staff”

also i am bit confution about following pharases

which sentense is correct

i will be assigning my duties in site office from next monday
i will assign my duties in site office from next monday


What do you mean by ‘assign’? Give your old duties to someone else?

"Assign"i mean taking over new responsibilities in new office, i think the sentence should be i will be attending…

my old duties…mange data & douments in a construction company , coordinate with contractors & clients,reporting to management about submission status…

I will be assuming my duties in the site office next Monday.