Something like this should work. You can also use synonyms, if the .... get a bit much:
;with cte
as
(SELECT
*
from
OPENQUERY(LinkedServer, 'SELECT * FROM employees')
)
UPDATE MSSQLDB.dbo.employer
SET
employer.employeescol1 = cte.employeescol1
FROM
MSSQLDB.dbo.employer
inner join
cte
on
cte.idemployees = employer.idemployee