Add extra weight to the front of the trailer. You can use weights or even install additional batteries.
Check the location of the weight on the trailer. If the weight is too close to the rear axle, it may reduce the weight of the tongue. Try moving the load closer to the front axle.
Figure out if you have the correct wheel balance on the trailer. If the wheels are not balanced correctly, it can cause improper weight distribution.
If you have the option, try changing the mounting position of the leaf springs. This may change the angle at which the leaf springs interact with the trailer and affect the weight distribution.
You may need to add additional leaf springs or install reinforced leaf springs to increase the lift of the trailer.