How to incorporate user defined functions into R shiny app

Question

I am making a R shiny app that will import a csv file, run the table through a user defined function, and displays a plot and table. I'm not able to share the actual function, but have put an example function below for reference in the code.

fun <- function(dataset){
  p_plot <- plot(dataset)

  mm_table <- lm(y~x, data=dataset)
  return (list(p_plot, mm_table))
}

dataset <- data.frame(x= 1:10, y=1:10)
fun(dataset)

So far, I have been able to make a shell for the app that has all the tabs and buttons I want.

library(shiny)
library(shinythemes)
library(dplyr)


ui <- shinyUI(fluidPage(
    theme = shinytheme("readable"),
    titlePanel("Plot Generator"),
    tabsetPanel(
        tabPanel("Upload File",
                 titlePanel("Upload Deisgn"),
                 sidebarLayout(
                     sidebarPanel(
                         fileInput('file1', 'Choose CSV File',
                                   accept=c('text/csv',
                                            'text/comma-separated-values,text/plain',
                                            '.csv')),

                         tags$br(),
                         checkboxInput('header', 'Header', TRUE),
                         radioButtons('sep', 'Separator',
                                      c(Comma=',',
                                        Semicolon=';',
                                        Tab='\t'),
                                      ','),
                         actionButton("action", "Evaluate Design")

                     ),
                     mainPanel(
                         tableOutput('contents')
                     )
                 )
        ),
        tabPanel("Plot",
                 
                 mainPanel(
                     plotOutput('p_plot'),
                     tableOutput('mm_table'),
                     )
                 )
        )

    )
)


server <- shinyServer(function(input, output, session) {

    data <- reactive({
        req(input$file1) 
        inFile <- input$file1

        df <- read.csv(inFile$datapath, header = input$header, sep = input$sep,
                       quote = input$quote)%>% mutate(across(where(is.character), as.factor))


        return(df)
    })

    output$contents <- renderTable({
        data()
    })

    
    output$mm_table <- renderTable({
        mm_table
    })
    
    output$p_plot <- renderPlot({
        p_plot

    })
})

shinyApp(ui, server)

I don't understand how to incorporate the user defined function I created. I want the evaluate design button to run the imported table through my function. Where do I put my function and then how can I call the return objects? I eventually want to create buttons that can change the default arguments, but I don't understand how to interact with the user defined function.

The output$mm_table and output$p_plot are place holders and I know it isn't correct. I don't know how to call return objects from a user defined function in general.

Any help with code, feedback, or online resources would be appreciated. Thanks.