How to sync data in a ros bag

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I'm trying to integrate a LiDAR unit with an INS (IMU+GPS) and as it seems there's no way to sync them together unless we're willing to let go of IMU data (only GPS data is output in NMEA format if they are connected). So we connected them separately to a laptop and recorded some sample data and here's the issue: They are not in sync and when I try to do LiDAR mapping in any application ( here's one as an example) I get misaligned point clouds and jerky movement!

I was wondering if there's a way read the bag file, synchronize the data and save it in a new bag?

I have looked into TimeSynchronizer here but I'm not sure how to apply it, or if it's what I need for this purpose at all.

Here's also a hacky script I came up with in Python, but it doesn't produce the desired result I guess the timings are too close or it's not the proper method at all:

def sync__to_current_timestamp(bag, output_path):
topic_list = ["/os_cloud_node/points", "/os_cloud_node/imu", "/imu/data", "/gnss"]
with rosbag.Bag(output_path + 'data_synced.bag', 'w') as outbag:
    bar = ChargingBar('Syncing', max=bag.get_message_count())
    for topic, msg, t in bag.read_messages():
        bar.next()
        if topic == "/tf" and msg.transforms:
            outbag.write(topic, msg, rospy.Time.now())
        elif topic in topic_list:
            msg.header.stamp = rospy.Time.now()
            outbag.write(topic, msg, rospy.Time.now())
    bar.finish()
    print("\n Done!")

Would appreciate any pointers.