Please follow the below steps to set static value for shipping address fields and set default values on checkout page.

Step 1: Create a module and in app/code/Magemonkeys/Customfield/di.xml put the below code in it.

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
    <type name="MagentoCheckoutBlockCheckoutLayoutProcessor">
        <plugin name="room_number" type="MagemonkeysCustomfieldPluginCheckoutModelLayoutProcessor" sortOrder="100"/>
    </type>
</config>

Step 2: Create a LayoutProcessor.php at this location app/code/Magemonkeys/Customfield/Plugin/Checkout/Model.

<?php

namespace MagemonkeysCustomfieldPluginCheckoutModel;

use MagentoCheckoutBlockCheckoutLayoutProcessor as ChekcoutLayerprocessor;

class LayoutProcessor
{

    public function afterProcess(ChekcoutLayerprocessor $subject, array $jsLayout)
    {
		
		

		$jsLayout['components']['checkout']['children']['steps']['children']['shipping-step']
            ['children']['shippingAddress']['children']['shipping-address-fieldset']['children']['street']['children'][0]['value'] = 'Street Name';
			
			
			$jsLayout['components']['checkout']['children']['steps']['children']['shipping-step']
            ['children']['shippingAddress']['children']['shipping-address-fieldset']['children']['city']['value'] = 'City Name';
			
			$jsLayout['components']['checkout']['children']['steps']['children']['shipping-step']
            ['children']['shippingAddress']['children']['shipping-address-fieldset']['children']['postcode']['value'] = '12345';
			
			$jsLayout['components']['checkout']['children']['steps']['children']['shipping-step']
            ['children']['shippingAddress']['children']['shipping-address-fieldset']['children']['region_id']['value'] = 14;
			
		

        $jsLayout['components']['checkout']['children']['steps']['children']['shipping-step']['children']
        ['shippingAddress']['children']['shipping-address-fieldset']['children']['room_number'] = [
            'component' => 'Magento_Ui/js/form/element/abstract',
            'config' => [
                'customScope' => 'shippingAddress',
                'template' => 'ui/form/field',
                'elementTmpl' => 'Magemonkeys_Customfield/form/room_button',
                'options' => [],
                'id' => 'room_number'
            ],
            'dataScope' => 'shippingAddress.room_number',
            'label' => 'Room Number if known',
            'provider' => 'checkoutProvider',
            'visible' => true,
            'validation' => [],
            'sortOrder' => 50,
            'id' => 'room_number'
        ];

        return $jsLayout;
    }
}