How do I manipulate data received from an API endpoint and submit to database - next.js

Question

The aim of my application is to take a URL submitted by a user in a form, pull data from it, manipulate that data, and then submit the manipulated data to a Postgres database.
Current Status
So far I have developed a form on the front end of the application (irrelevant validation / styling code has been removed from this excerpt):
const Feeds = ({ visible }) => {
const handleSubmit = async (e) => {
e.preventDefault();
try {
const body = { feedTitle, websiteUrl, currency, feedUrl };
await fetch('/api/form', {
method: 'POST',
headers: { 'Content-Type': 'application/json' },
body: JSON.stringify(body)
});
console.log('body: ', body);
} catch (error) {
console.error(error);
}
};
return (
<Form onSubmit={(e) => handleSubmit(e)} id="myForm" visible={visible}>
<HeaderContainer>
<Header>Add a new feed</Header>
<HeaderDescription>Please complete all of the required fields below and submit to add a new feed.</HeaderDescription>
</HeaderContainer>
<FormContainer>
<InputContainer>
<Label>Feed title</Label>
<Input type="text" placeholder="" value={feedTitle} onChange={(e) => handleChangeFeedTitle(e)} />
</InputContainer>
<InputContainer>
<Label>Website url</Label>
<Input type="text" placeholder="" value={websiteUrl} onChange={(e) => handleChangeWebsiteUrl(e)} />
</InputContainer>
<InputContainer>
<Label>Currency</Label>
<Select onChange={(e) => handleChangeCurrency(e)} name="currency" id="currency-select">
{currencies.map((option, index) => (
<option key={index} value={option.value}>
{option.text}
</option>
))}
</Select>
</InputContainer>
<InputContainer>
<Label>Feed url</Label>
<Input type="text" placeholder="" value={feedUrl} onChange={(e) => handleChangeFeedUrl(e)} />
</InputContainer>
</FormContainer>
{allValid ? <Button type="submit" form="myForm">Save</Button> : <DisabledButton>Save</DisabledButton>}
</Form>
)
};
export default Feeds;
On submission, this POST request hits the /api/form API endpoint:
const handler = async (req, res) => {
const body = req.body;
const response = await fetch(body.feedUrl)
.then(res => res.text())
.then(content => console.log(content))
.catch(err => console.error(err));
console.log('body: ', body);
res.status(200).json({ data: `${body}` })
};
export default handler;
Here I have simply console logged the content coming back from the API. Instead I need to manipulate it using a function and then submit the manipulated data to a database using a separate function.
The Problem
My question is, where should I implement these functions so that they trigger on the server side?
Thanks