Updating multiple mysql rows where column has specific value
create table temp with two fields your have in your csv and 

load data infile '/path/your.csv' into table temp FIELDS TERMINATED BY ‘,’ LINES TERMINATED BY ‘\n’;


then perform join

update wp_usermeta, temp set wp_usermeta.meta_value=temp.meta_value where wp_usermeta.user_id=temp.user_id;