magento-module/Block/Adminhtml/System/Config/Button.php

<?php
namespace Retailcrm\Retailcrm\Block\Adminhtml\System\Config;

class Button extends \Magento\Config\Block\System\Config\Form\Field
{
    /**
     * @var string
     */
    protected $_template = 'Retailcrm_Retailcrm::system/config/button.phtml';

    /**
     * @param \Magento\Backend\Block\Template\Context $context
     * @param array $data
     */
    public function __construct(
        \Magento\Backend\Block\Template\Context $context,
        array $data = []
    ) {
        parent::__construct($context, $data);
    }

    /**
     * Remove scope label
     *
     * @param  \Magento\Framework\Data\Form\Element\AbstractElement $element
     * @return string
     */
    public function render(\Magento\Framework\Data\Form\Element\AbstractElement $element)
    {
        $element->unsScope()->unsCanUseWebsiteValue()->unsCanUseDefaultValue();
        return parent::render($element);
    }

    /**
     * Return element html
     *
     * @param  \Magento\Framework\Data\Form\Element\AbstractElement $element
     * @return string
     *
     * @SuppressWarnings(PHPMD.UnusedFormalParameter)
     */
    protected function _getElementHtml(\Magento\Framework\Data\Form\Element\AbstractElement $element)
    {
        return $this->_toHtml();
    }

    /**
     * Return ajax url for synchronize button
     *
     * @return string
     */
    public function getAjaxSyncUrl()
    {
        return $this->getUrl('retailcrm_retailcrm/system_config/button');
    }

    /**
     * Generate synchronize button html
     *
     * @return string
     */
    public function getButtonHtml()
    {
        $button = $this->getLayout()->createBlock(
            'Magento\Backend\Block\Widget\Button'
        )->setData(
            [
                'id' => 'order_button',
                'label' => __('Run'),
            ]
        );

        return $button->toHtml();
    }
}