要重置Bcrypt哈希值，每当用户POST数据时，可以按照以下步骤进行解决：

1. 创建一个用户模型并存储密码的哈希值。

from flask_bcrypt import Bcrypt
from flask_sqlalchemy import SQLAlchemy

app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = 'your_database_uri'
db = SQLAlchemy(app)
bcrypt = Bcrypt(app)

class User(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    username = db.Column(db.String(80), unique=True, nullable=False)
    password = db.Column(db.String(120), nullable=False)

    def __init__(self, username, password):
        self.username = username
        self.password = bcrypt.generate_password_hash(password).decode('utf-8')

    def check_password(self, password):
        return bcrypt.check_password_hash(self.password, password)

db.create_all()

2. 在用户登录时，检查密码是否匹配。

@app.route('/login', methods=['POST'])
def login():
    username = request.form.get('username')
    password = request.form.get('password')

    user = User.query.filter_by(username=username).first()

    if user and user.check_password(password):
        # 登录成功
        return jsonify({'message': 'Login successful'})
    else:
        # 登录失败
        return jsonify({'message': 'Invalid credentials'})

3. 当用户想要更改密码时，更新密码的哈希值。

@app.route('/change-password', methods=['POST'])
def change_password():
    username = request.form.get('username')
    old_password = request.form.get('old_password')
    new_password = request.form.get('new_password')

    user = User.query.filter_by(username=username).first()

    if user and user.check_password(old_password):
        # 更新密码哈希值
        user.password = bcrypt.generate_password_hash(new_password).decode('utf-8')
        db.session.commit()
        return jsonify({'message': 'Password updated successfully'})
    else:
        return jsonify({'message': 'Invalid credentials'})

这样，当用户POST数据时，可以根据需要重置密码的哈希值，并确保用户的密码不再有效。