html5 by default in newer versions, just "from wtforms import DateField"

loan.py

@@ -1,7 +1,7 @@
 from wtforms import SubmitField, StringField, HiddenField, validators, TextAreaField
 from flask_wtf import FlaskForm
 from flask import request, render_template, redirect
-from wtforms.fields.html5 import DateField
+from wtforms import DateField
 from main import db, app, ma
 from datetime import date
 from sqlalchemy import Sequence