- Account has field
ingestDate__c
- You like to have a field
ingestDateTime__c
instead of ingestDate__c
and replace ingestDate__c
with ingestDateTime__c

cat ~/.soql/datetime.soql
SELECT Id, Name, ingestDate__c FROM Account WHERE ingestDate__c != NULL
sfdx mohanc:data:bulkapi:query -q ~/.soql/datetime.soql -u mohan.chinnappan.n.sel@gmail.com
"Id","Name","IngestDate__c"
"0014x00001JUIV3AAP","GenePoint","2023-07-27"
"Id","Name","IngestDateTime__c"
"0014x00001JUIV3AAP","GenePoint","2023-07-27"
sfdx mohanc:data:bulkapi:update -f ~/.soql/datetime.soql.csv -u mohan.chinnappan.n.sel@gmail.com -o Account
- Above operation will convert the date from IngestDate__c to datetime in IngestDateTime__c
- Find where used for this field
IngestDate__c
and replace it with IngestDateTime__c