magento system.xml api key manual insertion

Question

hi below is my small part of xml code for sms api, i api key and username, lets say api key = abcdefgh, username: 1234567 , url= https://www.google.com/

please help me to place these values in the below code as am new to xml i need this help

thanks in advance

<config>
<sections>
    <smsnotifications module="smsnotifications">
        <tab>service</tab>
        <label>SMS Notifications</label>
        <sort_order>9001</sort_order>
        <show_in_default>1</show_in_default>
        <show_in_website>0</show_in_website>
        <show_in_store>0</show_in_store>
        <groups>
            <sms_api_credentials module="smsnotifications">
                <label>API Credentials</label>
                <expanded>1</expanded>
                <sort_order>1</sort_order>
                <show_in_default>1</show_in_default>
                <show_in_website>0</show_in_website>
                <show_in_store>0</show_in_store>
                <comment><![CDATA[
                ]]></comment>
                <fields>
                    <gateway_url>
                        <label> SMS gateway url</label>
                        <validate>required-entry</validate>
                        <frontend_type>text</frontend_type>
                        <sort_order>1</sort_order>
                        <show_in_default>1</show_in_default>
                        <show_in_website>0</show_in_website>
                        <show_in_store>0</show_in_store>
                        <comment></comment>
                    </gateway_url>
                    <auth_token>
                        <label>Api Key</label>
                        <validate>required-entry</validate>
                        <frontend_type>text</frontend_type>
                        <sort_order>2</sort_order>
                        <show_in_default>1</show_in_default>
                        <show_in_website>0</show_in_website>
                        <show_in_store>0</show_in_store>
                        <comment></comment>
                    </auth_token>
                    <sender_name>
                        <label> SENDERID</label>
                        <validate>required-entry</validate>
                        <frontend_type>text</frontend_type>
                        <sort_order>3</sort_order>
                        <show_in_default>1</show_in_default>
                        <show_in_website>0</show_in_website>
                        <show_in_store>0</show_in_store>
                        <comment></comment>
                    </sender_name>
                </fields>
            </sms_api_credentials>

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