with open('oids.txt', 'r') as file:
    oids = file.readlines()
print(oids) # just to prove that it was converted to list of officeIds
# if you want to get rid of '\n' you should consider using oid.strip() function
with open('oids.xml', 'w') as file:
    file.write(f'<xml>')
    for oid in oids:
        file.write(f'<officeid>{oid}</officeid>\n')
    file.write(f'</xml>')