Valuation Method in Item

i have items more than 15000 …now i need to add ‘Default Material Request Type’ and ‘Valuation Method’ to all my items.
after importing excel using update records …it shows error with ‘Valuation Method’
error log:
Traceback (most recent call last):
File “/home/umoms/moms-bench/apps/frappe/frappe/core/doctype/data_import/”, line 396, in upload
File “/home/umoms/moms-bench/apps/frappe/frappe/model/”, line 260, in save
return self._save(*args, **kwargs)
File “/home/umoms/moms-bench/apps/frappe/frappe/model/”, line 299, in _save
File “/home/umoms/moms-bench/apps/frappe/frappe/model/”, line 466, in _validate
File “/home/umoms/moms-bench/apps/frappe/frappe/model/”, line 493, in validate_set_only_once
File “/home/umoms/moms-bench/apps/frappe/frappe/”, line 353, in throw
msgprint(msg, raise_exception=exc, title=title, indicator=‘red’)
File “/home/umoms/moms-bench/apps/frappe/frappe/”, line 339, in msgprint
File “/home/umoms/moms-bench/apps/frappe/frappe/”, line 312, in _raise_exception
raise raise_exception(msg)
CannotChangeConstantError: Value cannot be changed for Valuation Method

Have you created stock transactions for those items already? If so, you cannot change the Valuation method.

There is no stock transaction for those items. the fact is
i created an item without selecting as ‘Maintatin Stock’. Now i want to make it as stock item and also need to set
Default Material Request = “material transfer”
Valuation Method = “moving average”
here i able to select default material request. but text box for Valuation Method not displaying

Did you check the valuation method in stock settings?