@Fahmida Yeasmin

We can edit the posted Journal Entries using write method with context value.(check_move_validity=False)

First cancel the journal entry.

journal_entry_obj.button_cancel()

And Remove the existing line item one2many data and create new records in one2many table in account.move.line. Look at the below code.

for line in journal_entry_obj.line_ids:
    # Deleting the line_ids by passing the conlutext value for skipping the crdit and debit validation.
    line.sudo().with_context(check_move_validity=False).unlink()

# Updating one2many table data

data_line_dict = {
    "move_id": journal_entry_obj.id,
    "account_id": account_id,
    "partner_id": partner_id,
    "name": name,
    "debit": debit,
    "credit": credit,
    "company_id": journal_entry_obj.company_id.id,
    "company_currency_id": journal_entry_obj.company_id.currency_id.id,
    "currency_id": journal_entry_obj.currency_id.id,
}
self.env['account.move.line'].sudo().with_context(check_move_validity=False).create(data_line_dict)

and finally call the Reset to Draft and Post button

journal_entry_obj.button_draft()
journal_entry_obj.action_post()

It will work.

In Odoo 14.0 you can't delete them but you can add a customization to override unlink method of account.move model as below, so you can develop a custom module and override unlink method and then install it and delete the journal entries and then uninstall it if you don't need it.

 from odoo import models
class AccountMove(models.Model):
    _inherit = "account.move"

def unlink(self):
    for move in self:
        move.line_ids.unlink()
    return models.Model.unlink(self)