To change the step size in slider you need to open the control.js file from js folder and go to line 644. There you have the function wpestate_enable_slider();

Add the “step code ” after the value data in slider creation code . Should have something like
jQuery("#" + slider_name).slider({
range: true,
min: parseFloat(slider_min),
max: parseFloat(slider_max),
values: [price_low_val, price_max_val ],
step: 1000,

Screenshot from code in theme version 1.15.4

slider step

Note: this applies for shortocde, widget and mobile sliders as well.